JPS60100349A - Secondary electron detector - Google Patents

Abstract

PURPOSE:To pass and detect only the secondary electrons with specific energy by providing a Wien filter that intersects and applies a deflection electric field and a deflection magnetic field following a detector that detects the secondary electrons from a sample. CONSTITUTION:A sample 3 is irradiated with charged particle beams 1 tapered by a lens 2 and the secondary electrons are detected by a detector 6. In this case, a Wien filter that generates an electric field E and an magnetic field B by intersecting a deflection plate 13 and a deflection coil 14 is provided following a detector 16 and detects only the secondary electrons with specific energy through a diaphragm 15 by extracting the secondary electrons 51-53 from the sample 3 using a mesh 11 and making them incident on the filter. As a result, if a bandpass filter is provided, the resolution of secondary electron pictures can be improved and the cross-sectional pictures in the sample depth direction from a secondary electron generation mechanism can also be observed.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a secondary electron detector for a scanning electron microscope and similar devices, and particularly to a secondary electron detector suitable for detecting only secondary electrons having a specific energy. Regarding the detector.

[Background of the invention]

Conventional secondary electron detectors have only methods of detecting all 71c secondary electrons emitted from a sample, or detecting secondary electrons with higher energy than a specific energy. On the other hand, it was found that a secondary electron energy band-pass filter is effective for observing sample images with ultra-high resolution. (Details will be described later.) However, there has been no secondary electron detector equipped with a small band-pass filter that can be inserted between the sample and the secondary electron detector in a scanning electron microscope. This has caused problems in ultra-high resolution image observation.

The reason why the secondary electron energy bandpass filter is effective for ultra-high resolution image observation will be explained below using FIG. 1.

When an electron beam 102 is incident on a sample 101, the incident electron beam is scattered within the sample and spreads to about a boundary 103. At this time, this electron beam is absorbed or secondary electrons 104 are emitted. If all of these secondary electrons 104 are detected and image observed, the incident electron beam 102 will ideally be incident at one point.
Even if there are, there are about 20 people in the boundary 103, so the image resolution is limited to 20 people. However, if we consider the energy and quantity distribution of the emitted secondary electrons, we get the result as shown in Figure 2. Figure 2 shows the depth a+ of the sample in Figure 1.
b Each distribution of secondary electrons emitted from each region of HC a, b, c
J--Distribution 105 of total secondary electrons is shown. From this figure 2, it can be seen that if the sample image is observed only using secondary electrons with a specific energy of 10G, the proportion of secondary electrons emitted from the shallow region of the sample will be the highest, and the incident electron beam It was found that image resolution comparable to the diameter could be obtained.

In other words, it was found that a band-pass filter with secondary electron energy is extremely effective for ultra-high resolution image observation of 20 Å or less.

[Object of the Invention] An object of the present invention is to provide a secondary electron detector that detects only electrons having a specific energy of a secondary electron beam emitted from a sample. The object of the present invention is to provide a secondary electron detector with a so-called band-pass filter.

[Summary of the invention]

An energy filter may be added to the conventional secondary electron detector. However, it needs to be smaller than the mounting surface. Therefore, we decided to use a Wien filter (which applies a deflection electric field and a deflection magnetic field orthogonally and causes only electrons with a specific energy to travel straight), which is used as an energy filter.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. 3.4.

The primary electron beam 1 is narrowly focused by a lens 2 and irradiates the sample 3. The secondary electrons 5 emitted at this time are detected by a detector 6. The energy of secondary electrons is several eV, generally 1
Since the secondary electrons are about 2 to 4 orders of magnitude lower, by applying a small voltage to the detector 6, only the secondary electrons can be detected.
The secondary electrons can be left unaffected.

Conventionally, all of these secondary electrons were detected, but in the present invention, only secondary electrons with a certain energy are detected through an energy filter as shown in FIG. This will be explained below with reference to FIG.

The secondary electrons 51 to 53 emitted from the sample are exposed to the voltage V! applied to the mesh 11. attracted by.

Further, if a voltage V2f such that V2>Vt is applied to the cylinder 12, the secondary electrons heat the mesh 11.

Here, the deflection plate 13 and the deflection coil 14 are configured to be perpendicular to each other so that the electric current 1 and the magnetic field B are as shown in FIG. In other words, a Wien filter is formed. At this time, in the incident secondary electrons 51 to 53, e/Ill: ratio of electron charge to quality Fo: only secondary electrons with energy that satisfies the energy of the secondary electrons are deflected;
Go straight. (1) Let this secondary electron be 52 in Figure 4)
Lower energy (Fl)02 secondary electrons 5 and higher energy (Fz) (7) secondary electrons 53 are deflected as shown in the figure. Therefore, the aperture 15 allows the detector 16 to detect only the secondary electrons 52 having energy Fo. It goes without saying that by adjusting the magnetic field B and the magnetic field E, the value of the energy F0 of the secondary ′′ energy detected by the detector 16 can be arbitrarily selected.

In this example, when secondary electrons were detected under the following conditions, the energy detection sensitivity was approximately 1e.
I got V. That is, V+””50V.

V2=100V, B=100Gauta, E=58
7w (the distance between the deflection electrode plates was 10wn, and V3 = 290V), the electrode length (430mm), the distance between the electrode center and the aperture (z
) 100 degrees. Under these conditions, 1e is better than Fo.
The amount of deflection of secondary electrons with different V on the aperture is 4.3 Hu. In the experiment, the aperture 15 was used as a three-throat slit.

As a result, a detection sensitivity of about 1 eV was obtained. The above is very
It goes without saying that this is an example and is not limited to this. Further, a permanent magnet may be used instead of the deflection coil 14.

In the present invention, the deflection electric field and the magnetic field were directly fired, but this was done in order to align the center axis of the electrostatic deflection plate or deflection coil with the center axis of the detector, and only one of them was used. However, it can be used as an energy filter.

However, the central axes of the aperture 15 and the detector 16 must be shifted from the axes of the deflection plate and deflection coil.

In the example shown in FIG. 3 of the present invention, the detector 6 is disposed between the deflector 4 and the lens 2, but the present invention is not limited to this figure. In short, it is sufficient that an energy filter is placed in front of a conventional detector. [Effects of the Invention] According to the present invention, only secondary electrons can be detected with a specific energy when detecting secondary electrons. As a result, a cross-sectional image in the depth direction of the sample can be obtained from the secondary electron generation mechanism,
This has the effect of improving the resolution of the secondary electron image.

[Brief explanation of the drawing]

Figure 1 shows the scattering within the sample and the 2
FIG. 3 is a schematic diagram showing the state of secondary electron emission. FIG. 2 is a relationship curve diagram showing the distribution of secondary electron energy and its amount. FIG. 3 is a main S cross-sectional view of a scanning electron microscope showing one embodiment of the present invention. FIG. 4 is a sectional view of a secondary electron detector with an energy filter according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Primary' electron beam, 2... Lens, 3... Sample, 4... Deflector, 5... Secondary electron, 6... Detector, 11... Mesh, 12...Cylinder, 13...Electrostatic deflection plate, 14...Deflection coil, 15...Aperture, 16
...Detector, 51-53...■ 1 Fig. Z Fig. 1 UfJ 3 Fig. 4

Claims (1)

[Claims] 1. In an apparatus equipped with a detector that irradiates a sample with a finely focused charged particle beam and detects secondary electrons emitted from the sample, the charged particle beam has a specific energy just before the detector. A secondary electron detector characterized in that a means for allowing only secondary electrons to pass is provided. 2. The secondary electron detector according to item 1, wherein only secondary electrons having a specific energy are allowed to pass through using a deflection magnetic field or a deflection electric field and an aperture. 3. Applying a deflection magnetic field and a deflection electric field orthogonally,
2. The secondary electron detector according to claim 1, wherein only secondary electrons having a specific energy are allowed to pass through the aperture.